Hertfordshire has a
good history of monitoring numbers of breeding Rooks through spring counts of nests at
rookeries. Previous complete surveys were carried out in 1960-61, 1971, 1975 and 1993.
The Herts Bird Club is running a Rookery census during the 2015 breeding season.

Fieldwork
for the 2008-12 county breeding atlas showed a small increase in the number of tetrads in
which breeding was confirmed, but for a colonial nesting species, this does not necessarily
mean that the population has increased. This new census aims to estimate the population by
locating all rookeries within the county and counting the numbers of nests at least once
between mid-March and the end of April 2015.

There will be two components to the Herts Bird Club 2015 Rookery Census. The general
survey will aim to obtain a single count of the number of nests in all rookeries in the
county, whilst the special survey will gather more detailed information on a smaller
number of breeding colonies.